Proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a therapeutic target for the reduction of low-density lipoprotein cholesterol (LDL-C). PCSK9 increases the degradation of the LDL receptor, resulting in high LDL-C in individuals with high PCSK9 activity.
Lindholm et al., Molecular Therapy (2012); 20 2, 376-381 reports on two LNA antisense oligonucleotides targeting PCSK9 that produce sustained reduction of LDL-C in nonhuman primates after a loading dose (20 mg/kg) and four weekly maintenance doses (5 mg/kg). The compounds used were a 14mer SPC5001 (SEQ ID NO 1) and a 13mer SPC4061. SPC5001 is likewise disclosed in WO2011/009697. The efficacy of these PCSK9 inhibitors has been attributed to their short length (Krieg et al., Molecular Therapy Nucleic Acids (2012) 1, e6).
WO2007/146511 reports on short bicyclic (LNA) gapmer antisense oligonucleotides which apparently are more potent and less toxic than longer compounds. The exemplified compounds appear to be 14 nts in length.
According to van Poelgeest et al., (American Journal of Kidney Disease, 2013 October; 62(4):796-800), the administration of LNA antisense oligonucleotide SPC5001 in human clinical trials may result in acute kidney injury.
According to EP 1 984 381 B1, Seth et al., Nucleic Acids Symposium Series 2008 No. 52 553-554 and Swayze et al., Nucleic Acid Research 2007, vol 35, pp 687-700, LNA oligonucleotides cause significant hepatotoxicity in animals. According to WO2007/146511, the toxicity of LNA oligonucleotides may be avoided by using LNA gapmers as short as 12-14 nucleotides in length. EP 1 984 381 B1 recommends using 6′ substituted bicyclic nucleotides to decrease the hepatotoxicity potential of LNA oligonucleotides. According to Hagedorn et al., Nucleic Acid Therapeutics 2013, the hepatotoxic potential of antisense oligonucleotide may be predicted from their sequence and modification pattern.
Oligonucleotide conjugates have been extensively evaluated for use in siRNAs, where they are considered essential in order to obtain sufficient in vivo potency. For example, see WO2004/044141 refers to modified oligomeric compounds that modulate gene expression via an RNA interference pathway. The oligomeric compounds include one or more conjugate moieties that can modify or enhance the pharmacokinetic and pharmacodynamic properties of the attached oligomeric compound.
WO2012/083046 reports on a galactose cluster-pharmacokinetic modulator targeting moiety for siRNAs.
In contrast, single stranded antisense oligonucleotides are typically administered therapeutically without conjugation or formulation. The main target tissues for antisense oligonucleotides are the liver and the kidney, although a wide range of other tissues are also accessible by the antisense modality, including lymph node, spleen, and bone marrow.
WO 2005/086775 refers to targeted delivery of therapeutic agents to specific organs using a therapeutic chemical moiety, a cleavable linker and a labeling domain. The cleavable linker may be, for example, a disulfide group, a peptide or a restriction enzyme cleavable oligonucleotide domain.
WO 2011/126937 refers to targeted intracellular delivery of oligonucleotides via conjugation with small molecule ligands.
WO2009/025669 refers to polymeric (polyethylene glycol) linkers containing pyridyl disulphide moieties. See also Zhao et al., Bioconjugate Chem. 2005 16 758-766.
Chaltin et al., Bioconjugate Chem. 2005 16 827-836 reports on cholesterol modified mono-di- and tetrameric oligonucleotides used to incorporate antisense oligonucleotides into cationic liposomes, to produce a dendrimeric delivery system. Cholesterol is conjugated to the oligonucleotides via a lysine linker.
Other non-cleavable cholesterol conjugates have been used to target siRNAs and antagomirs to the liver—see for example, Soutscheck et al., Nature 2004 vol. 432 173-178 and Krützfeldt et al., Nature 2005 vol 438, 685-689. For the partially phosphorothiolated siRNAs and antagomirs, the use of cholesterol as a liver targeting entity was found to be essential for in vivo activity.